1. Field of the Invention
This invention relates to ink jet printing, and more particularly, to ink compositions for ink jet printers.
2. Description of the Related Art
Ink compositions, especially those for use with ink jet printers, must satisfy a number of conditions in order to achieve acceptable printing. Generally, it is desirable to provide good print quality. A fast drying ink composition is also desirable. However, fast drying inks tend to suffer from poor print quality due to feathering, intercolor bleeding, and the like.
The print quality of an ink may also be affected by the printing medium used. For example, paper is often sized with sizing components for the purpose of retarding or preventing penetration of liquids into the structure. This is commonly done by introducing a material to the pulp during the paper making operation. Paper may be sized internally or on the surface. Acid sizing chemicals, such as Mon size available from Monsanto Chemical Company or alkaline sizing chemicals such as Hercon-76 available from Hercules Company, are precipitated onto the fibers primarily for the purpose of controlling penetration of liquids into the final dry paper. This process is known as internal sizing. Surface sizing involves the application of dispersions of film-forming substances such as converted starches, gums and modified polymers to previously formed paper. Surface sizing imparts strength to the paper and thus high quality printing papers are often surface sized as well. These internally and surface sized papers, when used with an ink jet printer containing predominantly water based inks, yield images which have undesirable pronounced intercolor bleed. The extent of intercolor bleed is reduced slightly with papers which are internally sized with no surface sizing.
It has been attempted to make the pH of the ink strongly basic or to add a large amount of a surfactant to the ink. An ink which is strongly alkaline is dangerous when the ink is touched, and also involves the drawbacks that it does not fair well with respect to feathering and drying characteristics for papers in which certain kinds of sizing agents are employed. On the other hand, a large amount of surfactant may lead to adverse effects as well, such as feathering, poor ejectability from ink jet nozzles, and the like.
U.S. Pat. No. 4,352,691 to Owatari et al. discloses a liquid ink for printers comprising a chemical component which dissolves at least one of a fibrous material, sizing material, and a surface treatment material. The component is a strong basic material which permits the ink to penetrate through a paper and dry rapidly upon impact. The strong basic material is a strong alkali such as sodium or potassium hydroxide, which may react with a wetting agent such as glycerin to form an alkoxide. The pH of the ink is between about 10 and 14.
U.S. Pat. No. 4,932,515 to Koike et al. discloses a recording liquid composition comprising water, a water-soluble dye, and an organic solvent. The organic solvent can sufficiently dissolve the dye and rapidly precipitate the dye by evaporation of the water in the ink so that high quality printing on a paper with a high or low degree of sizing can be accomplished. The water soluble dye has a solubility of 5% by weight or less in the organic solvent. The organic solvent may include polyalkylene glycols, block copolymers of ethylene oxide and propylene oxide, and others, present in an amount from 2 to 70% by weight, preferably 5 to 65% by weight, and more preferably 10 to 60% by weight.
Ozaki et al, Fixing Time of Ink-Jet Inks on Plain Paper, SPIE Vol. 1079 Hard Copy Output (1989), pp. 384-388, discloses the use of glycols to dissolve sizing agents such as resins in order to improve drying times on plain paper, especially papers containing resin. The inks have a viscosity greater than 4cP and drying times greater than a few seconds. The amount of glycol is greater than 5 wt. %.
There remains a need for ink compositions that are useful in ink jet printing processes, including color printing processes.